- AboutThis should describe the systems research collaboration, and present the overall research goals of the new group.
- PeopleHere are the different labs in the SRC…
- PublicationsA page where you will find categorized publications!
- ProjectsA page where you will find our projects
- ResourcesVarious resources for prospective students, current students, alumni. Maybe put something here about life in NYC and at Columbia…
ACM Transactions on Computer Systems (TOCS), Volume 24, Issue 2, May 2006
As businesses continue to grow their World Wide Web presence, it is becoming increasingly vital for them to have quantitative measures of the mean client perceived response times of their web services. We present Certes (CliEnt Response Time Estimated by the Server), an online server-based mechanism that allows web servers to estimate mean client perceived re- sponse time, as if measured at the client. Certes is based on a model of TCP that quanti- fies the effect that connection drops have on mean client perceived response time by using three simple server-side measurements: connection drop rate, connection accept rate and con- nection completion rate. The mechanism does not require modifications to HTTP servers or web pages, does not rely on probing or third party sampling, and does not require client-side modifications or scripting. Certes can be used to estimate response times for any web content, not just HTML. We have implemented Certes and compared its response time estimates with those obtained with detailed client instrumentation. Our results demonstrate that Certes pro- vides accurate server-based estimates of mean client response times in HTTP 1.0/1.1 environ- ments, even with rapidly changing workloads. Certes runs online in constant time with very low overhead. It can be used at websites and server farms to verify compliance with service level objectives.
Proceedings of the 15th International World Wide Web Conference (WWW 2006), May 2006
Although web applications are gaining popularity on mo- bile wireless PDAs, web browsers on these systems can be quite slow and often lack adequate functionality to access many web sites. We have developed pTHINC, a PDA thin- client solution that leverages more powerful servers to run full-function web browsers and other application logic, then sends simple screen updates to the PDA for display. pTHINC uses server-side screen scaling to provide high-fidelity dis- play and seamless mobility across a broad range of different clients and screen sizes, including both portrait and land- scape viewing modes. pTHINC also leverages existing PDA control buttons to improve system usability and maximize available screen resolution for application display. We have implemented pTHINC on Windows Mobile and evaluated its performance on mobile wireless devices. Our results com- pared to local PDA web browsers and other thin-client ap- proaches demonstrate that pTHINC provides superior web browsing performance and is the only PDA thin client that effectively supports crucial browser helper applications such as video playback.
Proceedings of the 2006 IEEE Symposium on Security and Privacy (SP '06), May 2006
Many current systems allow data produced by potentially malicious sources to be mounted as a file system. File system code must check this data for dangerous values or invariant violations before using it. Because file system code typically runs inside the operating system kernel, even a single unchecked value can crash the machine or lead to an exploit. Unfortunately, validating file system images is complex: they form DAGs with complex dependency relationships across massive amounts of data bound together with intricate, undocumented assumptions. This paper shows how to automatically find bugs in such code using symbolic execution. Rather than running the code on manually-constructed concrete input, we instead run it on symbolic input that is initially allowed to be ``anything.'' As the code runs, it observes (tests) this input and thus constrains its possible values.
We generate test cases by solving these constraints for concrete values. The approach works well in practice: we checked the disk mounting code of three widely-used Linux file systems: ext2, ext3, and JFS and found bugs in all of them where malicious data could either cause a kernel panic or form the basis of a buffer overflow attack.
Operating Systems Review (OSR), April 2006
Operating system courses teach students much more when they provide hands-on kernel-level project experience with a real operating system. However, enabling a large class of students to do kernel development can be difficult. To ad- dress this problem, we created a virtual kernel development environment in which operating systems can be developed, debugged, and rebooted in a shared computer facility with- out affecting other users. Using virtual machines and remote display technology, our virtual kernel development labora- tory enables even distance learning students at remote loca- tions to participate in kernel development projects with on- campus students. We have successfully deployed and used our virtual kernel development environment together with the open-source Linux kernel to provide kernel-level project experiences for over nine hundred students in the introduc- tory operating system course at Columbia University.
Department of Computer Science, Columbia University Technical Report , CUCS-004-06, February 2006
We present Grouped Distributed Queues (GDQ ), the first proportional share scheduler for multiprocessor systems that, by using a distributed queue architecture, scales well with a large number of processors and processes. GDQ achieves accurate proportional fairness scheduling with only O(1) scheduling overhead. GDQ takes a novel approach to distributed queuing: instead of creating per-processor queues that need to be constantly balanced to achieve any measure of proportional sharing fairness, GDQ uses a simple group- ing strategy to organize processes into groups based on similar processor time allocation rights, and then assigns processors to groups based on aggregate group shares. Group membership of processes is static, and fairness is achieved by dynamically migrating processors among groups. The set of processors work- ing on a group use simple, low-overhead round-robin queues, while processor reallocation among groups is achieved using a new multiprocessor adaptation of the well-known Weighted Fair Queuing (WFQ ) algorithm. By commoditizing processors and decoupling their allocation from process scheduling, GDQ provides, with only constant scheduling cost, fairness within a constant of the ideal generalized processor sharing model for process weights with a fixed upper bound. We have implemented GDQ in Linux and measured its performance. Our experimental results show that GDQ has low overhead and scales well with the number of processors.
Ph.D. Thesis, Department of Computer Science, Columbia University, January 2006
Remote display provides a number of benefits, including ubiquitous access, thin-client computing, remote assistance and secure central management. In practice, it is crucial that remote display systems effectively support existing unmodified applications on commodity operating systems. However, commodity operating system environments have very differ- ent display architectures which impact how remote display can be implemented. This dissertation discusses the details of deploying remote display on commodity operating systems, including Linux(with X Window System) and Microsoft Windows. We focus on the implementation of a remote display system on Microsoft Windows and introduce several tech- niques, including kernel-user mode communication, a high throughput command channel, and efficient synchronization. With these techniques, we successfully implement an asynchronous remote display system on top of a synchronous local display system. Our work extends THINC, a virtual display architecture for remote display, from an X/Linux-only archi- tecture to one across X/Linux and Windows. We present the detailed algorithm we used for supporting a portable command processing pipeline across multiple commodity operating systems. Our experiment results demonstrate that our approach can achieve similar remote display performance on both X/Linux and Windows.
;login, December 2005
As computers become more ubiquitous in large corporate, government, and academic organizations, the cost of owning and maintaining them is becoming unmanageable. Computers are increasingly networked, which only complicates the management problem given the myriad of viruses and other attacks commonplace in todayâ€™s networks. Security problems can wreak havoc on an organizationâ€™s comput- ing infrastructure. To prevent this, software vendors frequently release patches that can be applied to address security and mainte- nance issues that have been discovered. This becomes a management nightmare for administrators who take care of large sets of machines.
Proceedings of the 19th Large Installation System Administration Conference (LISA 2005), December 2005
Patching, upgrading, and maintaining operating system software is a growing management complexity problem that can result in unacceptable system downtime. We introduce AutoPod, a system that enables unscheduled operating system updates while preserving application service availability. AutoPod provides a group of processes and associated users with an isolated machine- independent virtualized environment that is decoupled from the underlying operating system instance. This virtualized environment is integrated with a novel checkpoint-restart mechanism which allows processes to be suspended, resumed, and migrated across operating system kernel versions with different security and maintenance patches. AutoPod incorporates a system status service to determine when operating system patches need to be applied to the current host, then automatically migrates application services to another host to preserve their availability while the current host is updated and rebooted. We have implemented AutoPod on Linux without requiring any application or operating system kernel changes. Our measurements on real world desktop and server applications demonstrate that AutoPod imposes little overhead and provides sub-second suspend and resume times that can be an order of magnitude faster than starting applications after a system reboot. AutoPod enables systems to autonomically stay updated with relevant maintenance and security patches, while ensuring no loss of data and minimizing service disruption.
Proceedings of the 7th International Conference on Information and Communications Security (ICICS 2005), December 2005
Software that covertly monitors user actions, also known as spyware, has become a first-level security threat due to its ubiquity and the difficulty of detecting and removing it. Such software may be inadvertently installed by a user that is casually browsing the web, or may be purposely installed by an attacker or even the owner of a system. This is particularly problematic in the case of utility computing, early manifestations of which are Internet cafes and thin-client computing. Traditional trusted computing approaches offer a partial solution to this by significantly increasing the size of the trusted computing base (TCB) to include the operating system and other software. We examine the problem of protecting a user accessing specific services in such an environment. We focus on secure video broadcasts and remote desktop access when using any convenient, and often untrusted, terminal as two example appli- cations. We posit that, at least for such applications, the TCB can be confined to a suitably modified graphics processing unit (GPU). Specifically, to prevent spy- ware on untrusted clients from accessing the userâ€™s data, we restrict the boundary of trust to the clientâ€™s GPU by moving image decryption into GPUs. This allows us to leverage existing capabilities as opposed to designing a new component from scratch. We discuss the applicability of GPU-based decryption in the two scenarios. We identify limitations due to current GPU capabilities and propose straightf
Proceedings of the 1st ACM/IEEE Symposium on Architectures for Networking and Communications Systems (ANCS 2005), October 2005
We present Group Round-Robin (GRR) scheduling, a hybrid fair packet scheduling framework based on a grouping strategy that narrows down the traditional trade-off between fairness and com- putational complexity. GRR combines its grouping strategy with a specialized round-robin scheduling algorithm that utilizes the prop- erties of GRR groups to schedule flows within groups in a man- ner that provides O(1) bounds on fairness with only O(1) time complexity. Under the practical assumption that GRR employs a small constant number of groups, we apply GRR to popular fair queuing scheduling algorithms and show how GRR can be used to achieve constant bounds on fairness and time complexity for these algorithms. We also present and prove new results on the fairness bounds for several of these fair queuing algorithms using a consistent fairness measure. We analyze the behavior of GRR and present experimental results that demonstrate how GRR can be combined with existing scheduling algorithms to provide much lower scheduling overhead and more than an order of magnitude better scheduling accuracy in practice than scheduling algorithms without GRR.